HMO stands for Health Maintenance Organization. Health
Maintenance Organizations (HMOs) are only one of many
types of managed care arrangements. Individuals who join
an HMO are considered members. Typically HMOs provide
members with comprehensive health care including
preventative health services. When someone joins an HMO,
they select a primary care physician from the list
provided by the HMO. That primary care physician
coordinates all of that member's medical care. If care
by a specialist is needed, the primary care physician
will refer the member to a specialist who is usually
also in the HMO network. Members who go outside of the
network to receive care (unless given prior approval)
will probably pay all or most of the cost of that care
out of their own pockets.

Gail Carlson, MPH Ph.D.,
Continuing Medical Education, School of Medicine,
University of Missouri-Columbia